diff --git a/pkgs/sage-legacy-install-cleaner/setup.py b/pkgs/sage-legacy-install-cleaner/setup.py
index 7c843ddadee..51c9baadd13 100755
--- a/pkgs/sage-legacy-install-cleaner/setup.py
+++ b/pkgs/sage-legacy-install-cleaner/setup.py
@@ -9,6 +9,12 @@
 from distutils import log
 from setuptools import setup
 
+# Work around a Cython problem in Python 3.8.x on macOS
+# https://github.com/cython/cython/issues/3262
+if os.uname().sysname == 'Darwin':
+    import multiprocessing
+    multiprocessing.set_start_method('fork', force=True)
+
 #########################################################
 ### Set source directory
 #########################################################